Manufacture of fuze heads

ABSTRACT

Novel fuse heads and a process for making them in which a suspension of a primary explosive composition is made in water to which a small amount of one or more organic hydrophilic polymers is added in the proportion one to 10 percent by weight of the dry primary explosive composition. Bridge wires are immersed in the suspension and removed with the adhering material and the fuse heads so produced are allowed to dry.

Sieiies Peieiii [191 Thomas et a3: Oct. 9, 1973 [54] MANUFACTUZ'ZE 0FFUZE HEADS 3,415,189 12/1968 Trevorrow 102/28 M n e s Arwyu heep flugomas 66 3,586,551 6/197. Nolan 14 9/2 i 2 Giilmans Rd., Orpington;Raymond James Wiiiiams, 48 Langdaie Gar 1 S H b m f E I l d PrimaryExaminer- Verlm R. Pendegrass Gen We 0 0 pg an Attorney-Stevens, Davis,Miller & Mosher [22} Filed: July 9, 1971 {211 App]. No.: 161,259

Reieterl US. Appiicaiion Date Continuation-impart of Ser. No. 110,720,Jan. 28, 1971, abandoned.

{57] ABSTRAIT Novel fuse heads and a process for making them in which asuspension of a pn'mary explosive composition is made in water to whicha small amount of one or more organic hydrophilic polymers is added inthe proportion one to 10 percent by weight of the dry primary explosivecomposition. Bridge wires are im mersed in the suspension and removedwith the adhering material and the fuse heads so produced are allowed todry.

8 Cieims, 2 Drawing Figures initiiitiitiiiih "isinusitisihithm Thisapplication is a continuation-in-part of our application Ser. No. 110730filed 28th January, 197], and now abandoned.

This invention relates to improved fuseheads and to methods of makingthem.

Fuse heads are electrical detonating means in which a section of asuitable bridge wire is coated with a primary explosive composition anda binder, and which on passage of an electric current thorugh the coatedwire, ignite. They are normally made by immersing the bridge wire in asuspension. of the primary explosive composition, a portion of whichsticks on to and is retained by the wire as a bead. In order to obtainreproducible fuse heads, it is necessary to use a reasonably stablesuspension of a sufficient quantity of the primary explosive to permitknown quantities of the primary explosive composition to adhere to thewire. This has been achieved in the past by suspending the primaryexplosive composition in a suspension of nitrocellulose or ethylcellulose in an organic solvent such as an amyl acetate/amyl alcoholmixture. Normally, this involves a two-stage dipping process. Forexample, a fusehead may consist of a first layer derived from a mixtureof lead mono-nitro-resorcinate and potassium chlorate suspended in amixture of nitro-cellulose or ethyl cellulose in an organic solvent anda second layer derived from a mixture of potassium chlorate and charcoalin a similar organic solvent suspension. This method has thedisadvantages that the primary explosive must be handled dry, with theconsequent risk of explosion, prior to the mixing with thenitrocellulose or ethyl cellulose suspension and the organic solventbeing inflammable, greatly increases the hazards of the process.

Owing to the solubility of inorganic salts such as potassium chlorate inwater, it has not been feasible to use binders suspended or dispersed inwater to prepare fusehead dipping mixtures.

A further disadvantage of fuseheads incorporating nitrocellulose as abinder is that they should not be kept at temperatures above 100C as thenitrocellulose then becomes unstable.

it has now been found that fuseheads may be prepared employing aonestage dipping operation in a cheap and relatively safe way byimmersing a bridge wire in an aqueous suspension of a primary explosivecomposition to which a small amount of an organic h drophilic polymerhas been added.

According to the invention, there is provided a process for themanufacture of a fusehead comprising forming a suspension of a primaryexplosive composition in water containing a small amount of oneor moreorganic hydrophilic polymers (as hereinafter defined) in a proportionbetween about l to about l percent by weight of the dry primaryexplosive composition, immersing a bridge wire in said suspension,removing said bridge wire and adhering material and allowing thefnsehead so produced to dry.

Preferably the organic hydrophilic polymer is at least one of thecompounds methyl cellulose, sodium carboxy methyl cellulose andpolyvinyl alcohol.

The term organic hydrophilic polymer as used in this specificationrefers to an organic polymer which when added to water gives a viscouscolloidal dispersion or solution. it will he realised that the degree ofsubstitu may be affected not only by the concentration of the polymerbut also by the degree of substitution or the chain length of thepolymer. For instance, lower concentrations within the range I to 10percent ofa high molecular weight polymer can produce the same effect ashigher concentrations within the range of l to 10 percent of lowermolecular weight polymers.

The viscosity of the aqueous solution or dispersion of the organichydrophilic polymer must be such that this solution will retain as arelatively homogeneous suspension the particles or granules of theprimary explosive composition to be used for a period sufficiently longto prepare a worthwhile number of fuse heads without being re-mixed. Thebridgewire need only be immersed for a few seconds and this can be asimple dipping action or a sweeping action. It may be immersed for oneor more times depending on the concentration of the explosive in thesuspension and the amount of explosive composition required on thefusehead. The colloidal dispersion must not be a rigid gel as this wouldadversely affect the adhesion of the dispersion on the bridge wire andthe consistency of the bead size obtained.

The bulk density and the particle size of primary explosive compositionshave various values and this factor must be taken into account. Inaccordance with well known principles in the art, the proportion oforganic hydrophilic polymer in the aqueous suspension will need to behigher within the range 1 to 10 percent for compositions having higherbulk densities and/or larger particle sizes.

Fuseheads may be used for a variety of purposes including, for example,initiation of a detonator such as lead azide, ignition of a charge, forinstance a delay charge or a propellant charge, or for the purpose ofgenerating a gas pressure.

It will be realised that such applications require fuseheads givingdifferent output energies. The variation in the required output energiesmay be obtained by a compensating variation in the initiating propertiesof the fusehead as is well known in the art. in the fuseheads accordingto the invention this variation in initiating properties may be obtainedby a variation in the primary explosive composition and/or theproportion of the hydrophilic polymer incorporated in the fuseheadcomposition. For concentrations greater than 5 percent, fuseheads would,in general, be less energetic but may be more suitable for particularapplications such as the generation of a gas pressure. Too much polymercould render the resultant fusehead inert and a concentration of betweenI and 5 percent is generally preferable. A few simple tests wouldconfirm the required concentration of any specilic polymer within therange from about l-lO percent against the particle size/density of theprimary explosive, its specific function, and the mechanical propertiesof the fusehead produced.

ln this patent specification, the words primary explosive compositionare used to define a sparingly water soluble composition which may bereadily ignited by a hot wire. This composition may include fuels and/oroxidants in addition to the conventional explosives. Compositions whichmay be used include metal styph' nales such as the lead and bariumsalts, metal azides such as the lead and silver salts, the lead salts ofdiniand metal piorates such as the lead and potassium salts and includebeta monobasic lead styphnate, normal llitlll SI llfltllt, acid lead 4,6dinitr0res0rcinol, normal The fusehead consist of an insulating body 1made of pressboard which tapers slightly from the bottom 2 to the top 3.The top side 3 is partly cut away to leave a step 4. The sides of thebody 1 are covered with brassfoil attached to the body 1 by any knownmeans. A platinum wire 5 is stretched across the step 4 and securelyfastened to the brassfoil 5 by soldered joints 7. The upper end of thebody 1 and the wire 6 is covered by a bead of a primary explosivecomposition 8.

The invention is illustrated by the following examples:

EXAMPLE I The water content of wet beta monobasic lead styphnate ofparticle size approximately 6-10 microns long and 1-2 microns wide wasdetermined and sufficient material was weighed out to give 8.08g of thedry lead styphnate. The water content was adjusted to give a total watercontent of 2.0g. Srnl of an aqueous suspension containing 5 percent(wt/vol) of methyl cellulose (coagulation temperature 70C, viscosity of1 percent aqueous solution 10-20 cp) was added and the whole was mixedto give a smooth paste. Bridge wires were immersed in this paste,withdrawn and the formed fuseheads allowed to dry. The above paste wasused without further re-mixing up to about minutes with little variationin the composition and or bead size attained on the finished fuze-head.

EXAMPLE 2 The water content of wet beta monobasic lead styphnate wasdetermined and sufficient material weighed out to give 9.5g of the drylead styphnate. The water content was adjusted to give a total watercontent of 2.0g. 5.0ml of an aqueous suspension containing 10 percent(wt/vol) polyvinyl alcohol (99 percent hydrolysed, viscosity 4 percentaqueous solution 5-25cp) was added and the whole mixed to give a smoothpaste. Fuseheads were made as in Example I.

EXAMlLE 3 4.8g of finely divided lead azide (approximately l-S micronsdiameter) (prepared by precipitation) was taken and 2.5g of water addeclLOml of 10 percent (wt/vol) polyvinyl alcohol (99 percenthydrolysed,viscosity of 4 percent aqueous solution 5-25cp) was added andthe whole mixed to a smooth paste. By successive dipping operations,fuseheads containing up to 50mg of lead azide were made.

EXAMPLE 4 5.0g of beta monobasic lead styphnatc was taken and mixed with6.25mi of an 8 percent (wt/vol) aqueous polyvinyl alcohol (99 percenthydrolysed, viscosity of 4 percent aqueous solution 5-25cp) solution andthe whole mixed to give a smooth paste. Fuseheads made 4 from thissuspension exploded satisfactorily but had a low energy output.

The water content of monobasic lead azotetrazole (particle size, length10-20 microns, breadth 2-4 microns) was determined and sufficientmaterial weighed out to give 5.0g of dry salt. The water content wasadjusted to give a total water content of 1.3g. 4ml of an aqueoussuspension containing 2.5 percent (wt/vol) sodium carboxy methylcellulose (viscosity ofa 1 percent solution 20-35cp determined in a Utube) was added and the whole mixed to a smooth paste. Bridge wires wereimmersed in this solution, withdrawn and the formed fuseheads allowed todry.

EXAMPLE 6 5.0g of potassium picrate (average particle size 525 microns)was added to 3.0 ml of an aqueous suspension containing 5 percent(wt/vol) polyvinyl alcohol (as used in Example 2) and the whole mixed toa smooth paste. Fuse-heads prepared from this mix ignited readily andburnt quietly and completely.

EXAMPLE 7 The water content of wet acid lead salt of 4, 6-dinitroresorcinol (20-50 microns long, 1-2 microns wide) was determined andsufficient material weighed out to give 5.0 g of the dry salt. The watercontent was adjusted to give a total water content of 1.25g. 6.26 ml ofan aqueous suspension containing 3 percent (wt/vol) sodium carboxymethyl cellulose was added and the whole mixed to a smooth paste.Fuseheads prepared from this mix ignited readily and burnt quietly andcompletely.

EXAMPLE 8 The water content of a wet lead salt of trinitrophloroglucinol(5090 microns long, 2-4 microns wide) was determined and sufficientmaterial weighed out to give 5.0g of the dry salt. The water content wasadjusted to give a total water content of 1.5g. 5.0 ml of an aqueoussuspension containing 5 percent (wt/vol) methyl cellulose (as used inExample 1) was added and the whose mixed to a smooth paste. Fuseheadswere made from this mixture by the method given in Example 1.

Fuseheads prepared according to the invention are mechanically stableand suffer a negligible increase in weight due to absorbing water evenwhen stored for three months at ambient temperatures and 98 percentrelative humidity. There is no visible deterioration after heating at Cfor two hours and no deterioration when cooled at lgi}.

Although fuseheads made according to the invention show no tendency toabsorb moisture, they may finally be covered by a lacquer of ahydrophobic colioid.

The invention also provides novel fuseheads comprising a mixture of aprimary explosive composition and an organic hydrophilic polymer inwhich the proportion of the polymer is about one to about 10 percent byweight of the primary explosive composition.

What we claimed is:

1.. A fusehead having ignitable material comprising a primary explosivecomposition comprising ,8 monobasic lead styphnate and an organichydrophilic polymer wherein the proportion of the hydrophilic polymer iswithin the range from about 1 to about 10 percent the dry primaryexplosive composition.

' I l i use ea .avmgigma eml primary explosive composition comprisingmonobasic lead styphnate and an organic hydrophilic polymer wherein theproportion of the hydrophilic polymer is' 6. A fusehead according toclaim 2 wherein the organic hydrophiiic polymer is at least one of thegroup consisting of methyl cellulose, sodium carboxy methyl celluloseand polyvinyl alcohol.

7. A fusehead additionally comprises according to claim 2 wherein thefusehead a hydrophobic colloid cover.

8. A fusehead according to claim 2 wherein the primary explosivesubstance contains at least one compound selected from the groupconsisting of fuels and oxidants.

UNITED STATES PATENT OFFICE- CERTIFICATE OF CORRECTION Patent No.763,783 Dated October 9, 1973 lfiye t THOMAS et al 'It is certified thaterror appears in the above-identified patent and vthat said LettersPatent are hereby corrected as shown below:

Col. 1,;line 11, change "thorugh" to through-. Col. 3," line 17, change"wire 5" to wire 6-. Col. 4, line 43, change "whose" to whole-. Col. 51,line 12, Claim 4, after "comprises" delete "covline 13, after "coloid"insert cover-.

In clai'ni 7, col 6,"line' 7, delete "additionally compris-- es" i line8, after "fusehead" insert -'additionally comprises r.

Signed and sealed this Znd day of July i974.

(SEAL) Attest EDWARD M. FLEICHE R, JR. C. MARSHALL DANN AttestingOfficer Commissioner of Patents USCOMM-DC 603 5-96) FORM F'O-IOSO(10-69) ORM PO-1050 (10-69) Attest:

Patent No. 3 r 7.6- 783 Dated October 9, 1973 Inventofls) THOMAS. et alCol. Col.

Col.

It is certified that error appears in the above-identified patent v andvthat said Letters Patent are hereby corrected as shown below:

line line line li-ne "line In claiin 7, col

" line comprises:-fl-.

EDWARD M. FLETCHER, JR. Attesting Officer 11, change "thorugh" tothrough--. l7, change "wire 5" to wire 6. 43, change "whose" to whole.

12, Claim 4, after "comprises" delete "covafter "coloid" insert cover-.

6, line 7,' delete "additionally compris- 8, after."fusehead" insert--additio'n ally c. MARSHALL DANN I Commissioner of Patents USCOMM-DC0037 5-969

2. A fusehead having ignitable material comprising a primary explosivecomposition comprising Beta monobasic lead styphnate and an organichydrophilic polymer wherein the proportion of the hydrophilic polymer iswithin the range from about 1 to about 5 percent of the dry primaryexplosive composition.
 3. A fusehead according to claim 1 wherein theorganic hydrophilic polymer is at least one of the group consisting ofmethyl cellulose, sodium carboxy methyl cellulose and polyvinyl alcohol.4. A fusehead according to claim 1 wherein the fusehead additionallycomprises a hydrophobic colloid cover.
 5. A fusehead according to claim1 wherein the primary explosive substance contains at least one compoundselected from the group consisting of fuels and oxidants.
 6. A fuseheadaccording to claim 2 wherein the organic hydrophilic polymer is at leastone of the group consisting of methyl cellulose, sodium carboxy methylcellulose and polyvinyl alcohol.
 7. A fusehead according to claim 2wherein the fusehead additionally comprises a hydrophobic colloid cover.8. A fusehead according to claim 2 wherein the primary explosivesubstance contains at least one compound selected from the groupconsisting of fuels and oxidants.